A123792 Number of ways to build a contiguous building with n LEGO blocks of size 1 X 5 on top of a fixed block of the same size so that the building is flat, i.e., with all blocks in parallel position.

9, 91, 1089, 13726, 182736, 2493062, 34865595, 495114895, 7127585291

Offset

1,1

Comments

The base block is not counted among the n and must be the only block in the bottom layer of the building.

Links

Table of n, a(n) for n=1..9.

Crossrefs

Cf. A112389, A123762 - A123827, A123829 - A123849.

Sequence in context: A335508 A176735 A286786 * A022520 A020236 A068624

Adjacent sequences: A123789 A123790 A123791 * A123793 A123794 A123795

Keyword

nonn,hard

Author

Søren Eilers, Oct 29 2006

Status

approved